2002 Avalanche 5.3 O! M! G!

Well, thankfully the problem followed the O2 sensor. Lucky me it wasn't the signal wire. Thank God

OK... got the O2 problems straightened out. I found out there are 2 style of O2 S1 sensors for this truck. I had the Canada O2 sensors in which my truck wasn't built there. It shouldn't make a difference but it does. This is why the first set of O2 sensors oddly didn't work. Trims got slightly better because the correct sensors are in. But I still have one bank LT at 25 and the other is like 21 at idle.

I also removed the kinks in the fuel supply line... so it wasn't that. Damn it.

Here the following reading:

At Idle STFT Bank1 = 1%, STFT Bank2 = 4%, LTFT Bank1 = 24%, LTFT Bank2 = 16%

At 1000 rpm STFT Bank1 = 7%, STFT Bank2 = 5%, LTFT Bank1 = 21%, LTFT Bank2 = 14%

At 2000 rpm STFT Bank1 = 3%, STFT Bank2 = 6%, LTFT Bank1 = 17%, LTFT Bank2 = 8%

At 3000 rpm STFT Bank1 = 19%, STFT Bank2 = 14%, LTFT Bank1 = 3%, LTFT Bank2 = 1%

Truck does run better now that all the O2's are working properly and goes into Closed Loop. Would a leaky exhaust manifold gasket cause these problems since I can't find a vacuum leak. Cause while getting into the gas pedal going down the road I thought I heard an exhaust leak from the right side, passenger side, while racing the motor in passing gear but both Long Terms are maxed not just one side.

Thanks

I have to try that check that hakachukai had mentioned.

You really need to solve your cylinder 6 ( bank 2 ) low compression problem.


EDIT
I misread the fuel trims above as negative. I don't know why. Sorry about that.
That makes everything that I said below irrelevant:
[hr]

Bank2 is running more rich than bank1 probably because of all of the raw fuel flying down the pipe from cylinder 6 not being able to burn it properly.

However, both banks are running rich.

Assuming that your fuel pressure is still around 50psi:
You previously mentioned replacing your injectors with higher flow injectors. Maybe try putting the original injectors back in and see if that solves your rich problem.
[hr]
END EDIT

This part still applies:
[hr]
I'd also do an EGR bypass just to simplify things. I recently found out how much a leaking EGR valve can seriously mess with your fuel trims.
If it's the flange type, just unbolt it, cut a gasket for it that has no hole and bolt it back down ( for diagnostic purposed only ). DON'T leave it like that.

Fixing exhaust leaks never hurts either. The easiest way I know of to find those is the start it up and let it idle while reasonably plugging the tail pipe with some cloth ( or something like that ).

If you have no leak, pressure will build in the exhaust until it either blows the cloth out, or the engine stalls.
If you do have a leak, it will be super easy to find because of the pressure. Just crawl under there and look for the exhaust shooting out of the pipe sideways.

Thanks hakachukai… I have to check the EGR valve as you mentioned... plus what kind of ass designed the pcv valve as part of the valve cover?

Well, we can rule out the EGR valve because that engine that year didn't come with one. It's like deciphering it's history... lol

Lolz!

Welcome to Automechanics!

5 parts machinery
3 parts electrical pixies
2 parts chemistry
1 part history professor

Ain't that the truth... LMAO!!! It took me long to reply with info cause I had to wait to get paid and my back went out on me. The work I'm used to is following after someone else's work, fixing their mistakes, blah blah blah. What I'm not used to is the factory just all of a sudden not doing something that they are used to doing for decades. I guess it's better engineering, I guess... lol. It took me, a couple of weeks ago, a few minutes to try and remove the pcv valve which is now part of the valve cover. I think since I can't check the pcv valve I can at least clamp that hose off that goes from the intake manifold to the pcv valve off to see if fuel trims get better or not.

Lol, I feel like I'm at step #1 again in figuring this stupid truck out. I actually am after getting that O2 problem fingered out

what you're testing when you pinch off the PCV hose is for an internal intake air leak. Check for vacuum in the dipstick tube when doing the test.

chevy/gmc 5.3L are known for an oil consumption issue due to the PCV valve and the baffle in the valve cover.

you still have a vacuum leak... your LTFT's get better with higher RPM.

air entering through the exhaust manifold can cause the 02's to read lean. when doing the exhaust check (putting a rag in the tail pipe) check the fuel trims. if they go to 0 or start correcting, that is a leak that you have to repair. any air leak in the exhaust prior to the 02 will effect the 02 reading.

with those positive LTFT's of 21 and 24 at idle, I think its more likely you have an internal intake leak. that's if you're sure you have no external vacuum leaks.

Thanks for keeping me on the straight and narrow

I was going to ask if your fuel trim numbers were negative or those were just dashes in front of the numbers? I'm with scannerjohn on this with a vacuum leak if those are not negative numbers.

Nissan Technician

I also assumed that those dashes were negative signs. If they are not... then forget almost everything that I said.

Really sorry about that guys... the - is meant to be = not negative numbers. Again sorry didn't mean for that to throw everyone off.

I edited one of my posts above because I messed up. Sorry about that.

Well, Went and plugged the PCV vacuum line... nothing. Pinched off the Vacuum assist line to the brakes... nothing. Brought my scanner out by the engine and started spraying brake cleaner looking for leaks... nothing. This truck is really kicking me in the butt. I'm going to pull out my little smoke machine since it's a very nice day out with hardly any wind. Maybe I'll see some smoke somewhere today. I also checked the exhaust for leaks like scanner john said... nothing as far as I could tell. Nothing was obvious I should say.

SJ where else would an internal leak be? I'm really at a lost now. I checked for exhaust leaks incompletely... I was by myself and was basically listening for leak. I'll have my wife help me later with the scanner.

the internal leak would be at the intake manifold gasket bottom side of the manifold. you will not be able to use water, propane or brake cleaner to detect the leak as its internal. the presence of vacuum in the dipstick tube is caused by that leak. if you changed the intake gasket, it may have not sealed correctly.

Thanks for the heads up on the leak. I haven't changed that gasket yet because I saw no smoke. and I forgot to check the dip stick for vacuum. Just a thought... would I have to block off the Pcv valve? That would create vacuum at the dip stick too wouldn't it?

Another thought.... what if I pulled the dip stick out and run another smoke test? It should come out the dipstick tube wouldn't it?

Thanks again

you clamp off the PCV hose and the fresh air inlet PCV tube(passanger side front of the engine). when you run the engine this would produce pressure at the dipstick, but if you have an internal intake gasket leak you will have vacuum at the dipstick instead. smoke will not work because your checking for vacuum not pressure. the leak would be pulling extra air in from the crankcase into the intake runner causing a lean condition.